AEDs are used by police officers, paramedics and other first-response emergency medical personnel to resuscitate cardiac arrest patients. As such, AFDs are typically used in responding to a 911 call (or a call to another local emergency number). Upon the receipt of such an emergency call, an emergency medical system (EMS) is usually activated, which then dispatches EMS personnel to the scene. EMS personnel are then responsible for reaching the patient and using the AED to defibrillate the patient. After cardiac stabilization the patient is usually transported to the hospital.
In order to adequately assess the response times and efficiencies of an emergency medical system, it is necessary to track the time between the receipt of the 911 call and the time at which care is first administered to the patient. Typically, the response time is calculated by comparing the time of the 911 call (as recorded on the 911 emergency computer) to the time of the first shock delivery (as recorded on the internal real time clock on the ALD). Unfortunately, it is often difficult to accurately measure this time due to inherent problems of comparing times on two independent clocks. This is especially true as the internal clock in an AED may differ with time relative to the 911 clock. As a result, the response times measured through the AED real time clock often included errors of many minutes. The magnitude of this error is extremely significant in light of studies which indicate that the chances for successful resuscitation diminish approximately ten percent per elapsed response minute. Accordingly, it is evident that there is a need for increased accuracy in measuring response times using AEDs.